Mitral insufficiency can result from several causes, such as ischemic disease, degenerative disease of the mitral apparatus, rheumatic fever, endocarditis, congenital heart disease and cardiomyopathy. The four major structural components of the mitral valve are the annulus, the two leaflets, the chordae and the papillary muscles. Any one or all of these in different combinations may be injured and create insufficiency. Annular dilation is a major component in the pathology of mitral insufficiency regardless of cause. Moreover, many patients have a mitral insufficiency primarily or exclusively due to posterior annular dilation, since the annulus of the anterior leaflet does not dilate because it is anchored to the fibrous skeleton of the base of the heart.
Studies of the natural history of mitral insufficiency have found that totally asymptomatic patients with severe mitral insufficiency usually progress to severe disability within five years. Currently, the treatment consists of either mitral valve replacements or repair, both methods requiring open heart surgery. Replacement can be performed with either mechanical or biological valves.
The mechanical valve carries the risk of thromboembolism and requires anticoagulation, with all its potential hazards, whereas biological prostheses suffer from limited durability. Another hazard with replacement is the risk of endocarditis. These risks and other valve related complications are greatly diminished with valve repair.
Mitral valve repair theoretically is possible if an essentially normal anterior leaflet is present. The basic four techniques of repair include the use of an annuloplasty ring, quadrangular segmental resection of diseased posterior leaflet, shortening of elongated chordae, and transposition of posterior leaflet chordae to the anterior leaflet.
Annuloplasty rings are needed to achieve a durable reduction of the annular dilation. All the common rings are sutured along the posterior mitral leaflet adjacent to the mitral annulus in the left atrium. The Duran ring encircles the valve completely, whereas the others are open towards the anterior leaflet. The ring can either be rigid, like the original Carpentier ring, or flexible but non-elastic, like the Duran ring or the Cosgrove-Edwards ring.
Effective treatment of mitral insufficiency currently requires open-heart surgery, by the use of total cardiopulmonary bypass, aortic cross-clamping and cardioplegic cardiac arrest. To certain groups of patients, this is particularly hazardous. Elderly patients, patients with a poor left ventricular function, renal disease, severe calcification of the aorta, and those having previous cardiac surgery or other concomitant diseases would in particular most likely benefit from a less invasive approach, even if repair is not complete.
Such a less invasive method is proposed in U.S. Pat. No. 6,210,432, which describes a method for treatment of mitral insufficiency without the need for cardiopulmonary by-pass and opening of the chest and heart. The method uses a device comprising an elongate body having such dimensions as to be insertable into the coronary sinus, which is a vein that substantially encircles the mitral orifice and annulus and drains blood from the myocardium to the right atrium. The elongate body has two states, in a first of which the elongate body has a shape that is adaptable to the shape of the coronary sinus, and to the second of which the elongate body is transferable from said first state assuming a reduced radius of curvature. Consequently, the radius of curvature of the coronary sinus is reduced. Due to the coronary sinus encircling the mitral annulus, the radius of curvature as well as the circumference of the mitral annulus are reduced. Thus, the described method takes advantage of the position of the coronary sinus being close to the mitral annulus, which makes repair possible by the use of current catheter-guided techniques.
According to one method described in U.S. Pat. No. 6,210,432, a device comprising an elongate stent is used. The elongate stent includes hooks which are arranged to dig into the walls of the coronary sinus, by means of the surgeon retracting a cover sheet from the stent, in order to fix the position of the stent in the coronary sinus. A stabilizing instrument is used for keeping the elongate stent in its first state and then, after the hooks have dug into the walls, releasing it to its second state assuming a reduced radius of curvature. However, the position fixation of the elongate stent in the coronary sinus by means of the hooks might be insufficient, so that the sudden release of the contraction of the elongate stent dislocates it. This dislocation of the device might result in unsatisfactory reduction of the circumference of the mitral annulus.
According to an alternative method described in U.S. Pat. No. 6,210,432 the device comprises three stent sections that are positioned in the coronary sinus and connected by wires. The wires may be maneuvered from outside the vein system such that the distances between the adjacent stent sections are reduced. Also with this method there is a risk of dislocation of the device, since the surgeon might accidentally move insufficiently fixed stent sections out of their proper position while manipulating them from outside the vein system.
In view of these drawbacks of previously known treatments, it would be desirable to provide a minimally invasive approach to treat mitral insufficiency, i.e., without the need for cardiopulmonary bypass and without opening of the chest and heart.
It also would be desirable to provide a reduction of the mitral annulus using only catheter based technology.
It further would be desirable to provide a treatment for mitral insufficiency that minimizes trauma to a patient's vasculature while using catheter based technology.